Jaw-dropping skeleton find at The Capricorn Caves

HISTORIC: Heidi Van Der Meer, from Capricorn Caves, at the dig site where the discovery of a small reptile bone has proved to be a historic find.Rokccaves

IT'S the moments that make a palaeoecologist's jaw drop, and that's exactly what happened at The Capricorn Caves when a tiny fossil found during a two-metre deep excavation in 2012 proved to be from a giant lizard.

Capricorn Caves manager Ann Augusteyn said the study, published in Quaternary Science Reviews, highlighted her team's huge responsibility to care for the caves.

"This study also begs the question - what else is entombed in our caves and what else can we learn?," she said.

The Capricorn Caves house millions of bones and scientists say it could be Australia's most fossil-rich site.

University of Queensland vertebrate palaeoecologist Dr Gilbert Price said scientists could only hypothesise how the giant lizard bone made its way inside the cave, which contains bones of many rodents, regurgitated by owls.

Dr Price said researchers working in Central Queensland were amazed when they unearthed the first evidence that Australia's early human inhabitants and giant apex predator lizards had overlapped.

"Our jaws dropped when we found the tiny fossil from a giant lizard," he said.

"The one-centimetre bone, an osteoderm, came from under the lizard's skin and is the youngest record of a giant lizard on the entire continent."

Dr Price and his colleagues used radiocarbon and uranium thorium techniques to date the bone as about 50,000 years old, coinciding with the arrival of Australia's Aboriginal inhabitants.

"We can't tell if the bone is from a Komodo dragon - which once roamed Australia - or an even bigger species like the extinct Megalania monitor lizard, which weighed about 500kg and grew up to six metres long," he said.

"The find is pretty significant, especially for the timeframe that it dates."

The largest living lizard in Australia today is the perentie, which can grow up to two metres long.

Dr Price said massive lizards and even nine-metre long inland crocodiles roamed Australia during the last Ice Age in the Pleistocene geological period.

"It's been long-debated whether or not humans or climate change knocked off the giant lizards, alongside the rest of the megafauna," he said.

"Humans can only now be considered as potential drivers of their extinction."

A crew of volunteer citizen scientists helped with the research by sorting and sieving specimens.